The Nigerian Stock Exchange All Share Index fell 3.7 percent on Wednesday to 25,072.66 by 2:22 p.m. in Lagos, the lowest level since September 2012 and the most among 93 global indexes tracked by Bloomberg after Egypt. The measure is down 12 percent since the previous peak on Dec. 31, more than the 10 percent drop that indicates a market correction.

“The major factor is the oil price that has weakened further,” Pabina Yinkere, an analyst at Vetiva Capital Management Ltd., said by phone from Lagos. “That has implications for the nation as an oil-dependent country. It has created a heightened risk environment.”

Nigeria, Africa’s largest oil producer, is struggling to cope with crude oil prices that have fallen to below about $31 a barrel. Oil accounts for two-thirds of government revenue and about 90 percent of its foreign currency earnings. The slump is weighing on growth, which is estimated to have slowed tolow to 3.2 percent last year, the slowest pace this century, according to a Bloomberg survey of economists.

Currency Problem

Nigerian authorities are also facing mounting pressure to devalue the naira, which John Ashbourne, a London-based Africa economist at Capital Economics, said is strangling economic growth. The Abuja-based central bank has held the naira at 197 to 199 per dollar since March as Governor Godwin Emefiele introduced trading curbs to conserve reserves and stem a rout after it fell to a record 206.32 in February.

“We are having a currency problem,” Vetiva’s Yinkere said. “Investors are asking how this will be affecting organisations such as the banks that have slowed the issuing of letters of credit and manufacturers that are having difficulty accessing foreign exchange for imports.’’ Nigerian Breweries Plc dropped 4.9 percent, falling for an eighth day to the lowest since June 2012, and the biggest drain on the all-share index. Zenith Bank Plc slid 8.9 percent to a six-year low, while Nestle Nigeria Plc declined 5 percent, the most since Aug. 28.

Prices on three-month naira forwards gained 1.6 percent to 247 per dollar on Wednesday, rebounding from a record low. The currency, which is pegged at 197 per dollar by the central bank, weakened 0.3 percent at 199.05 on the interbank market.

The Central Bank of Nigeria this week lifted a ban on dollar cash deposits, ending a six-month embargo on banks from receiving dollar deposits from customers, and stopped selling foreign currency to money changers in an effort to maintain its reserves.

“The CBN will only supply the banks with an amount equivalent to the foreign exchange accruing at the CBN to finance priority imports, currently equivalent to about $1 billion per month,” JF Ruhashyankiko, an economist at Goldman Sachs Group Inc. in London, said in a Jan. 12 note. “As a result, and contrary to the consensus expectation of a devaluation in the first quarter of 2016, a further decline in oil prices is likely to translate into lower dollar supply to banks and a higher shadow exchange rate rather than a devaluation.”

The naira will probably remain at 200 per dollar for the next six months, weakening to 240 in the next 12 months, he said.